The present disclosure generally relates to a device for acquiring a blood sample and, in particular, to a device for acquiring a blood sample, which has a lancet, a puncture drive having drive spring, and a control unit for controlling the rapid piercing and retraction movement of the lancet.
In general, all diabetics need some sort of a device for the regular self-check of the blood sugar level. For this purpose, typically, the tip of a lancet is driven into the skin of a body part, preferably into a fingertip. A small quantity of blood exits from the wound, which is received either directly or by a capillary in the lancet. This blood sample can subsequently be analyzed.
The prior art, in general, is geared toward automatic handheld devices having integrated measuring units and lancets implemented as micro-needles having capillaries, which are implemented as disposables. A supply of disposable lancets is stored in a magazine. The replacement of a used lancet with a new one is performed automatically, so that the user does not have to handle individual parts.
For example, WO 2007/073870 describes a micro-sampler piercing system, whose puncture drive comprises a coiled spring, which propels a pushrod. The head of the pushrod can be coupled to the lancet. The movement of the lancet in the axial direction follows a predetermined movement profile and comprises a propulsion phase, during which the lancet pierces up to a predetermined maximum piercing depth, and a retraction phase immediately following, during which the lancet is retracted up to a predetermined residual piercing depth. Specifically, it has been established that the residual piercing depth is of great significance for optimum sample acquisition and the least possible pain. At the end of the propulsion phase, the pushrod contacts a stop. The drive spring is overstretched, so that the pushrod having the lancet coupled on can also be retracted again during the subsequent retraction phase. Alternatively, the puncture drive comprises a torsion spring, a tension rotor, and a drive rotor driven by the tensioned spring. A control apparatus in the form of a curve controller is used to convert the rotational movement of the drive motor into a linear piercing and retraction movement of a puncture element. A lancet control curve is implemented as a groove in the drive rotor and is followed by a control curve rider, which is connected to the lancet holder.
U.S. Pat. No. 6,206,901 B1 describes a blood sampling device having a lancet, which is driven via a tappet, and a drive spring. The lancet is decoupled from the drive spring for a part of its propulsion phase. In order to retract the lancet from the wound again after the piercing, a second spring is provided. This retraction spring is first tensioned during the propulsion phase, in that kinetic energy of the lancet is stored in the spring and, after reaching the maximum tension of the retraction spring, is returned to the lancet thereby. It is disadvantageous that the lancet is prematurely decelerated by the retraction spring. The entry of the lancet into the skin of the patient is thus slower and more painful.
EP 0 036 443 B1 also describes a lancet device in which the lancet is decoupled from the drive spring during a part of the puncture movement. The retraction of the lancet after the piercing is performed by a second spring, which is tensioned by the lancet during its propulsion movement.
Typically, puncture drives having a drive spring, whose spring force is transmitted linearly in the piercing direction directly to the lancet, have a simple construction and are thus also reliable and cost-effective, and additionally space-saving. They particularly allow installation in a narrow handheld device, which can be handled comfortably and easily by the user. In order to ensure the most rapid possible piercing with the least possible pain, rather strong springs are used. The danger exists that the needle will pierce multiple times due to post-oscillation. For example, in the blood sampling system according to EP 1 852 069 A 1, an oscillation control unit is provided, which acts on the vibratory system made of lancet and drive spring so that multiple piercing is prevented. Three types of action on the oscillation behavior of the lancet are described: on the one hand, a displaceable stop can delimit the oscillation movement of the lancet in the piercing direction. As a second possibility, a damping unit can be provided, for example, in the form of a hydraulic or pneumatic damper. As a further possibility, a location displacement of the drive spring can be provided, by which the zero point of the oscillation of the drive spring is displaced so that even at maximum deflection of the drive spring, further piercing of the lancet is prevented. The oscillation itself is not influenced. In micro-sampler puncture devices, which contain a supply of disposable lancets, in addition to the actual puncture drive, executes short, rapid forward and back movements, a mechanism, which provides comparatively slow, but long actuation strokes, in order to dock the magazined lancets to the puncture drive and release them again after a single use, must also be provided. Therefore, puncture drives, whose control unit works with a control curve, are fundamentally well suitable for alternating rapid and slow movement phases. However, they also have the disadvantage during long strokes that are comparatively large, because otherwise the pitch angles of the control curve grow up to self-inhibition.
If the puncture drive is simply equipped with a mechanical stop which delimits the maximum piercing depth, a hard impact occurs at the moment of the deepest piercing, which not only causes an irritating noise, but also triggers an oscillation of the needle, which results in an increased pain sensation.
The use of a crank drive in a puncture drive is known in the art, see, e.g., U.S. Pat. No. 4,924,879. The drive spring can be implemented therein as a coiled spring and can act directly on a crank wheel, so that it can rotate. The rotation of the crank wheel can then be converted by a pushrod into a linear movement of the lancet. The force flow in the propulsion phase can thus be precisely reversed from the design according to the present disclosure, in which firstly the drive spring can propel the lancet in the piercing direction and the crank drive can be driven passively.
Therefore, there is a need for a device for acquiring a blood sample that has a constructively simple puncture drive with a single drive spring acting in the direction of the movement axis of the lancet that has oscillation-free piercing. There is an additional need for a puncture drive for use in a framework of a slide mechanism to be used for the slow, complete retraction of the lancet, for docking and releasing magazined disposable lancets, and/or for tensioning the drive spring.